evidencija-rezija/email-worker/src/routes/errorRouter.ts

import { ErrorRequestHandler, Request, Response } from "express";
import createHttpError, { HttpError } from "http-errors";
import { createLogger } from '../lib/logger';
import { NgitLocals } from "../types/NgitLocals";
import { failedRequestCounter } from "../lib/metricsCounters";
import { SupportedRoutes } from "../types/enums/SupportedRoutes";

const consoleLog = createLogger("server:server");

/**
 * Router koji se zadnji poziva, a koji sastavlja odgovor u slučaju greške
 * @param err 
 * @param req 
 * @param res 
 * @param next 
 */
export const errorRouter:ErrorRequestHandler = async (err:HttpError, req, res, next) => {

    const requestPath = req.path as SupportedRoutes;

    // kako je ovaj error handler dosta složen, moguće je da negdje baci grešku
    // > zato je zamotan u try-catch
    // > na taj način osiguravam da neće srušiti cijeli proces
    try {

        let { name:errorLogName, message:errorLogText } = err;
        let responseBody:string = "";

        switch(err.status) {
            case 400:
                responseBody = 'bad request';
                break;
            case 401:
                responseBody = 'unauthorized';
                break;
            case 403:
                responseBody = 'forbidden';
                break;
            case 404:
                consoleLog(`page not found ${req.method} ${requestPath}`)
                responseBody = 'page not found';
                errorLogText = `page ${requestPath} not found`;
                break;
            case 500:
                responseBody = "internal server error";
                errorLogText = err.message;
                break;
            default:
                responseBody = err.name;
                errorLogText = `err.status=${err.status};err.name=${err.name};err.message=${err.message}`;
        }

        consoleLog(`${errorLogName}:${errorLogText}`);
        
        // `headersSent` će biti TRUE ako je router kod kojeg se dogodila greška već poslao header-e
        // > ako ih probam ponovo postaviti, to će baciti grešku ... a to ovdje mogu izbjeći
        if(!res.headersSent) {
            res.status(err.status);
            res.setHeader('Content-Type', "text/html");
            res.end(responseBody);
        } else {
            // AKO nije pozvan `end` - pozovi ga i završi obradu zahtjeva
            // ... u suprotnom će konekcija ostati otvorena do timeout-a
            if(!res.writableEnded) {
                res.end();
            }
        }

    } catch(ex:any) {
        // ovu grešku će obraditi `finalErrorRouter`
        next(createHttpError(500, ex));
    }

    // ne mogu dopustiti da prometheus client sruši server
    try  {
        failedRequestCounter.inc({ path: requestPath, status: err.status });
        (res.locals as NgitLocals).stopPrometheusTimer({ path: req.path, status: err.status });
    } catch(ex:any) {
        console.error(ex);
    }
};